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Insect Police Crack Down on Slackers

Like workaholic employees, worker bees, ants, and wasps give up families of their own for the good of the hive. But every company has its cheats, and some workers try to sneak eggs of their own into the queen's brood. That chutzpah puts their peers in a tizzy, and researchers have long thought that the outrage stemmed from blood loyalty to the queen. A new study, however, casts doubt on that theory.

In many species of social insects, workers try to lay eggs on the side, says evolutionary biologist Laurent Keller of the University of Lausanne, Switzerland. The unfertilized eggs develop into males, which can then abandon the colony and find a queen of their own. Usually, a police force of other workers cracks down on these freeloading co-workers by killing them or eating their illegal eggs. Accepted wisdom among sociobiologists has always been that such policing happens because workers are more related (and hence more loyal) to their queen's offspring than to other workers' sons.

To test this hypothesis, Keller and his colleague Robert Hammond combed the scientific literature for data on 50 species of ants, wasps, and bees. For each, they recorded the proportion of working-class males in the royal brood and the average number of males a queen mates with. When queens have many consorts, workers are less related to the bastard sons of other workers (their half-nephews) than when the queen mates just once. (In that case, the workers are full sisters, and their sons are full nephews.) So policing ought to be especially evident in species in which the queen is a swinger. But, as the researchers report in next week's Public Library of Science, Biology, they found no such relationship: The numbers of males produced by workers was independent of the colony's family ties. Keller thinks the real reason behind policing may be that egg-laying workers are slacking off on their regular chores, to the colony's detriment.

Evolutionary biologist Heike Feldhaar, who studies ants at the University of Würzburg, Germany, says the new study is interesting because it highlights the growing awareness that factors other than just relatedness are important in the lifestyle of social insects.